This invention is concerned with electronic printers of the non-impact type. As used throughout this specification, including the claims, the term electronic printer encompasses those printers in which information concerning the text to be printed is supplied electronically. Examples of systems that would have use of electronic printers are facsimile machines, word processors and computers.
In electronic printers of the non-impact type that contain a sump for holding print material, means is usually provided for automatically replenishing print material, such as ink or toner, as the print material is consumed. As an example, in an ink jet printer a sump is provided for holding liquid ink that is used during the printing operation. There is usually some type of measuring device to determine how much ink remains in the sump and filling means for providing additional print material to the sump as it is consumed. In a xerographic printer that uses dry, two component development powder, a sump also is provided which periodically must be supplied with replacement toner. The replacement of print material in such systems is either performed randomly or through a method of measuring the quantity of printing material remaining and replenishing it. With particular reference to a printer using the xerographic process and where a dry, two component toner is used in combination with a magnetic brush, random feeding is usually the case. More specifically, in an electronic printing operation wherein a xerographic printing process is utilized, an image is created on a photoconductive surface, as for example, through either exposure to light emitting diodes (LEDS) or through laser beam exposure. In either case, the image is created by the exposure to light in accordance with information stored in a memory and supplied therefrom to the imaging electronics. Typical of such a system, a hopper containing the toner is stationed over the sump of a magnetic brush unit and a rotary member containing pockets is located at the bottom of the hopper and rotates to supply material to the sump. The rotation of such rotary member is controlled by the operation of the printer and bears no relationship to the toner being consumed during the development of the image. As a consequence, since there is no relationship between the amount of print material being consumed and the amount of material that is supplied, variations in the density of the printed matter occur. Another means for replacing consumed toner is a toner density controller wherein the ratio of toner to carrier particles is measured. When the percentage of toner drops below a given level, the toner is replenished. As is known, such toner density controllers are expensive and generally lack accuracy. Obviously, it would be desirable to have a direct correlation between the amount of print material being consumed by an electronic printer and the amount supplied for the printing operation.